An Adaptive Digital Dynamic Range Controller

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Abstract

High fidelity digital audio sources are capable of reproducing a much wider dynamic range
than most conventional consumer media (e.g. AM/FM radio and audio cassettes). The
research presented here addresses the problem of matching this wide dynamic range to
that of a device ( or channel) with lower dynamic range capabilities using a Dynamic
Range Controller (DRC). Currently available digital signal processing hardware allows
the implementation of entirely Digital DRC's (DDRC's) that interface directly to digital
sources and eliminate unnecessary data (analog +--> digital) conversions.
The DDRC design presented in this thesis uses an adaptive level measurement scheme
and an adaptive recovery time to improve performance. The perceived distortion introduced
by rapid gain reductions (attack) is lessened by allowing attacks only at the zero
crossing preceding a transient. A single-channel version of the Adaptive DDRC has been
implemented for real-time operation on a DSP56000 evaluation board.
Tests showed that the Adaptive DDRC has insignificant total harmonic distortion.
Intermodulation distortion measurements compare favourably with a previous DDRC
design [11] that was reported as having good subjective performance. The results of our
listening tests show great promise for the Adaptive DDRC. Listeners rated the average
sound quality of an Adaptive DDRC configuration higher than a conventional design
(with peak level gain control). However, since other Adaptive DDRC configurations (i.e.
different parameter sets) did not perform as well, further testing is required to optimize
the Adaptive DDRC parameter set.